Dynamic optimisation of WWTP inflow to reduce total emission.

A prerequisite for an integrated control of sewer and wastewater treatment plant (WWTP) is a capacity driven inflow control to WWTP. This requires reliable information about the current status of WWTP operation and its behaviour on varying hydraulic, COD and nutrient loads. So far most of the proposed control strategies are based on hypothetical modelling studies. In this paper the behaviour of three large WWTPs on increased storm water loads is analysed based on online measurements of several years. In all cases the main limiting factors for an increase of load were the sedimentation processes in the secondary clarifier and the nitrification capacity. In one case study predictive control strategies have been developed observing these processes which are backboned by effluent control. Tests using an integrated model of sewer and WWTP demonstrate that inflow control on emission load varies significantly with rain intensity.

Integrated operation of sewer system and WWTP by simulation-based control of the WWTP inflow.

In recent years numerical modelling became a standard procedure to optimise urban wastewater systems design and operation by integration. For dynamic control of the wastewater teatment plant (WWTP) inflow, a model-based predictive concept is introduced aiming at improving the receiving water quality. An on-line simulator running parallel to the real WWTP operation reflects the actual state of operation and provides this model information to a prognosis tool which determines the best option for the WWTP inflow. The investigations showed that it is possible to reduce the NH4-N peak concentrations in the receiving water by dynamic WWTP inflow control based on predictive scenario analysis.

Online-simulation of the WWTP to minimise the total emission of WWTP and sewer system.

In this paper, the application of a WWTP-Online-Simulation with the objective to reduce the total emission into the receiving waters is explained. Apart from an introduction and a short description of the possible reduction potentials, first results of the current research project (financed by the German ministry BMBF) are presented. Results of the pilot plant with different experiments of increased stormwater inflow than usual and different control strategies showed the possibility to treat stormwater up to the quadruple dry-weather flow while still meeting the effluent values. However, this is not always guaranteed, and thus a monitoring system with integrated control strategies which is adapted to the load case "stormwater" with prognosis load cases becomes necessary. In the presented example, the simulation (Activated Sludge Model 2d) achieved an excellent match with the measured effluent values of the aeration tank (NH4-N, NO3-N) over a period of several months. The most important prerequisites for good (online-) simulation results are the exact knowledge of the plant and the plausibility and alternative concepts for the measured values in case of sensor failure.

Integrated modelling as an analytical and optimisation tool for urban watershed management.

In recent years numerical modelling has become a standard procedure to optimise urban wastewater systems design and operation. Since the models were developed for the subsystems independently, they did not support an integrated view to the operation of the sewer system, the wastewater treatment plant (WWTP) and the receiving water. After pointing out the benefits of an integrated approach and the possible synergy effects that may arise from analysing the interactions across the interfaces, three examples of modelling case studies carried out in Germany are introduced. With these examples we intend to demonstrate the potential of integrated models, though their development cannot be considered completed. They are set up with different combinations of self-developed and commercially available software. The aim is to analyse fluxes through the total wastewater system or to integrate pollution-based control in the upstream direction, that is e.g. managing the combined water retention tanks as a function of state variables in the WWTP or the receiving water. Furthermore the interface between the sewer and the WWTP can be optimised by predictive simulations such that the combined water flow can be maximised according to the time- and dynamics-dependent state of the treatment processes.